A great deal of effort has been expended in the search for satisfactory yarn piecing-up devices which will facilitate the efficient connection between a tail end of previously spun yarn with fibres fed to the spinning means.
For example, in British Pat. No. 1 444 497 a piecing-up device is disclosed which is in portable form so that it can be coupled to the machine at a defective spinning station where yarn piecing is required. The device includes a yarn reserve forming member in the form of a retractable pin around which the yarn extending from the package is passed so as to form a reserve length of yarn in the path between the yarn delivery rollers and the package. Upon actuation of the device, the pin is retracted out of the path of the yarn and in a direction transverse thereto so as to permit the yarn to return to the normal spinning path.
It is believed that such a piecing-up device would not operate to a satisfactory degree of efficiency, because of the lack of control over the yarn and its pathway or yarnline as it returns to the normal spinning path and into the delivery roller nip. After the yarn has been released from the pin, the reserve length of yarn is unsupported whilst it is eliminated by accumulation of the yarn on the package and by returning the end of yarn into the spinning means. Furthermore, there is uncertainty introduced as to precisely when the yarn will enter the delivery roller nip, and this uncertainty is increased because the yarn and its pathway or yarnline are uncontrolled and thus not prescribable during its return from the extended yarn path to the normal spinning path. If the yarn enters the delivery roller nip at indeterminate, which is to say unpredictable and uncontrollable, times during the piecing-up procedure, then the critical, precise moment of commencement of delivery of yarn from the spinning means is also indeterminate.
A further piecing-up device is disclosed in British Pat. No. 1 457 741 which is provided with two reserve length supporting members so that a first reserve length of yarn is formed between the delivery rollers and the package, and a second reserve length of yarn formed between the delivery rollers and the spinning means. The reserve lengths are released by removal of the supporting members and permitting the yarn to return to the normal spinning path in an uncontrolled manner.
The supporting members for the reserve length of yarn are positioned outside the length of the nip line defined by the delivery rollers and it has been found necessary to provide a mechanism having a guide which is movable so as to positively place the yarn into the delivery roller nip. Although this mechanism does provide some predictability as to the moment when delivery of yarn from the spinning means will be resumed, it adds to the complication of the device, and to its cost.
British Pat. No. 1 291 900 discloses a further piecing-up mechanism utilising a reserve length of yarn which can be reduced so as to permit the end of yarn to return to the spinning means to effect the piecing.
The support for the reserve length of yarn is a pin protruding from a rotatable disc to which it is attached. When the disc is rotated the pin remains in contact with the yarn and thereby exercises some control over the yarn as it returns to the normal spinning path.
In the arrangement shown in this specification, the yarn is placed in the delivery roller nip before releasing the reserve length of yarn and is thus applicable only to piecing-up during a starting of all the stations of the machine. Since piecing-up of a broken yarn at an individual station has to take place with the delivery rollers in rotation, this known arrangement is unsuitable for such situations.